1. Field of the Invention
The present invention relates generally to a locking device using permanent magnets. More particularly, the present invention relates to a locking device of the foregoing type which assures that a door can reliably be locked to an opposing door frame once the door is closed.
2. Description of the Related Art
A conventional automatic locking device is generally similar to a latch bolt in that an inclined surface is formed on the head of a so-called dead bolt for locking a door to an opposing door frame, the dead bolt is wedged into a lock box when the inclined surface of the dead bolt contacts a strike member fitted to the door frame as the door is being closed, and when the door is closed, the dead bolt is inserted into a hole in the door frame under the resilient force of a spring.
This device can malfunction when the dead bolt is not forced completely into the lock box by the strike member when the door is incorrectly fitted to the door frame or a closer does not properly operate. In these cases, it is obvious that the door will not be completely locked to the door frame. In the case in which the door is locked using an automatic locking device, a person usually goes outside through the opened door without confirming whether the door automatically locks to the door frame after he leave because he unconsciously believes that the door will be automatically closed. Such a malfunction is unacceptable.